This invention relates to photoelectric sensors and in particular to through beam photoelectric sensors. Still more particularly, the invention relates to through beam photoelectric sensors which are ganged together in a common housing.
The need for sensing and the use of sensors for monitoring conditions in manufacturing and processing functions is markedly increasing as the controls for such functions become more complex and rapidly responsive to changing conditions of the functions. As a result, manufacturing and processing apparatus incorporate a large number of sensor devices, often in small and remote locations within the apparatus. The size of individual sensors has been decreasing which enables them to be mounted in smaller spaces, but often the number of sensors which may be mounted within a given space is limited by the mounting hardware for the sensors. As a result, several sensors are mounted in a common housing for monitoring several sensing stations which are in close proximity to each other. For example, it may be desired to monitor the density of a liquid flowing in several closely spaced transparent conduits or to monitor the presence of absence or other condition of multiple strands of material, e.g. wire strands from a wire drawing apparatus or the like. In such applications where a through beam photoelectric sensor is used, it is often difficult to interrupt the material to be sensed when installing the sensing apparatus.